1. Field of the Invention
The present invention relates to means for mounting work tools, such as cutter bits, in the holders of machinery used in mining, excavating and earth working for presenting the bits in proper working position so that they can be driven against the face of the material to be worked.
2. Description of the Prior Art
U.S. Pat. No. 3,342,531, issued Sept. 19, 1967, to Krekeler, shows cutter bits held within mounting blocks by resilient retainers whereby the cutting bit is rotatable within the mounting block. The retaining means include spring wires, lug members, and the like.
U.S. Pat. No. 3,519,309, issued July 7, 1970, to Engle et al shows cutting bits which are retained within a mounting block by metal, split-rings having a pluralilty of dimple-like projections thereon. The metal ring is itself captive on the bit shank but freely rotatable thereon.
U.S. Pat. No. 4,201,421, issued May 6, 1980, to Den Besten et al shows a cutter bit mounted within a mounting block by a split, spring sleeve which is non-rotatable within the mounting block.
The above described keeper mechanisms primarily involve the use of a metal sleeve, ring, or the like, which is carried in a retaining groove on the bit shank and which snap into a region of enlarged diameter within the mounting block to retain the bit shank in the block. The retaining means are carried loosely on the bit shank to allow the bit shank some degree of rotation within the mounting block during cutting operation. The shank holding capabilities of the above described retainers are sometimes adversely affected because the shank becomes worn during use and is more loosely accommodated within the mounting block opening. With other of the prior designs, the retaining mechanism works adequately but cannot be easily removed when the time comes to replace the cutting element in the mounting block.
U.S. Pat. No. 3,767,266, issued Oct. 23, 1973, to Krekeler shows a resilient keeper ring made from plastic which is used to retain a cutter within a mounting block. The resilient ring is generally cylindrical and has a pair of end rims joined by parallel ribs having a series of angularly disposed, outwardly protruding rib-like portions. The parallel ribs form a web-like structure which flattens out during installation of the bit shank within the mounting block but snaps back to form an abutment surface which is retained against a shoulder in the moutning block to hold the cutter in position during the cutting operation. To remove the cutter, the shank is driven in the opposite direction. At this time, the webs are intended to again flatten out so that the bit shank can be removed form the mounting block opening. This design has proved problematical in that the dirt and other debris lodges between the shank exterior and internal diameter of the mounting block opening which keeps the resilient webs from collapsing and makes the shank difficult to remove.